OT impedance question

[g-man]

Deleted

[Dave]

I have heard a lot of hooplah about how using the "highest" tap is better because it uses all the windings.
I have also heard some people who really believe and swear that using the smallest tap IE 4ohm tap w/ 4ohm load gives more volume/fullness.
Experience has yet to confirm any of that for me.

Dave

[jjasilli]

Parallel speaker wiring is better functionally, because if one speaker blows there is still a load on the amp.  

Tonally it is theoretically possible that using less of the OT may allow it to saturate more or earlier.  Saturation is a thicker sound.  Blues guitar & harp players would probably tend to like that, but not everyone.  It's subjective.

[alerich]

Every Marshall 2204/2203 amplifier I have ever owned sounded better using the 16 ohm tap with a 16 ohm load. I don't know why but they have. I have always assumed that this was due to the oft mentioned phenomena of using all the secondary windings. Better is hard to describe - maybe a fuller sound with better bottom end.  It's been a while since I owned one of those amps.

[kagliostro]

In real world windings of transformers didn't give the exact impedance they are labeled

so I think you must try some different combination with your amp and speaker and chose which give the best result for you

Kagliostro

[jeff]

Parallel speaker wiring is better functionally, because if one speaker blows there is still a load on the amp.  

I've often wondered about this. Say you have a 100W amp and four 25W speakers in parallel. One blows, now you have 100W into a 75W cab so you blow another. Now you have 100W into 50W cab then another etc. until all your speakers are blown. You might be able to catch it in time if you hear the difference between 3 and 4 speakers and realize what's happening, but if you wire two sets of speakers in series and wire those in parallel the most you can blow is two out of four.

As far as which sounds better, rig a series/parallel switch in your cab to switch two sets of paralleled speakers either parallel for 4 or series for 16. Switch the switch and output jack at the same time to compare which you like better. See for yourself. Experience is better than theory. No one can answer this for you. It's like asking which is better, humbuckers or single coils, you need to find the one you like best.

[HotBluePlates]

I've often wondered about this. Say you have a 100W amp and four 25W speakers in parallel. One blows, now you have 100W into a 75W cab so you blow another. Now you have 100W into 50W cab then another etc. until all your speakers are blown. You might be able to catch it in time if you hear the difference between 3 and 4 speakers and realize what's happening, but if you wire two sets of speakers in series and wire those in parallel the most you can blow is two out of four.

Even with a 100w amp, you might not be sending a continuous 100w to the speakers, due to the complex nature of a guitar signal. 100w continuous is more likely with keyboards, organs, and a sine test signal. I bet a lot of keyboard players use more "speaker power" than amp power.

Exception: When you apply a square wave to a speaker. If you calculate the "peak power" of a 100w RMS sine wave, it is 200w peak power. But peak power is not informative with a sine wave, just like we say "120vac" not 169.7v peak (except in certain cases). But if you are talking about a square wave, because the wave stays at its peak for exactly half of the cycle (assumine 50% duty cycle), the peak power is equal to RMS power, and 200w peak equals 200w continuous.

I notice I've never blown a speaker, and that the guys I know that have all played metal, and used distortion pedals so heavey-handed, they probably turned the guitar signal into a close approximation of a square wave.

[PRR]

> One blows...you blow another ...then another etc. until all your speakers are blown.

That's the way I see it too.

Since the invention of hi-temp coil-glue, the answer is to rate the speaker generously. Your 4-speaker 100W rig can use 50W or 100W speakers, lots of safety margin.

> Even with a 100w amp, you might not be sending a continuous 100w to the speakers, due to the complex nature of a guitar signal.

Undistorted speech/music, a "100W" amp puts 10 Watts or less average heat to the speaker.

DisTORTed, a healthy "100W" amp can put 200 Watts of heat in the speaker. (My SE 6550 would make 13W clean sine 16W sorta-bent sine-like, but 23 Watts of near-square power, limiting my testbench runs with a 20W dummy load.)

In practice, in "music", you will rarely hold total-clipping square wave for many seconds.

The GUITAR speaker makers know this. A "25 Watt" speaker will take 50 Watts of heat for many minutes. Read the amp's power claim and buy a for-guitar speaker claiming something more.

OTOH, Hi-Fi speakers are NOT rated for heavy clipping. A "100 Watt" hi-fi woofer may melt in 5 minutes of 25 real Watts. (Tweeters rarely stand 10 Watts for long-- you MUST filter-off the heavy lows and strong mids.)

[jojokeo]

OTOH, Hi-Fi speakers are NOT rated for heavy clipping. A "100 Watt" hi-fi woofer may melt in 5 minutes of 25 real Watts. (Tweeters rarely stand 10 Watts for long-- you MUST filter-off the heavy lows and strong mids.)

  Reminds me of when in the early 70's mom & dad bought me my first electric geetar, a LP Goldtop copy but I had no amp. I plugged straight into the - back then $2000+ hi-fi Pioneer stereo system we had. I blew those expensive 3-way Altec Lansing speakers badly! That's when we discovered Orange County Speaker w/ their re-coning service which was only a 10 minute drive away. Almost immediately afterwards I got my first '63 Tremolux. But then it only took about a year before I blew those speakers too    I've been back to OC Speaker many times ever since and can say they do a great job and are highly recommended.

Back on subject: Fender liked their speakers in parallel wired for 2ohms in many amps while Marshall liked the 16ohm set-up...no right or wrong way.

[firemedic]

I think the original question was, does a multi-tap secondary sound better using the highest impedance since it is using all the secondary windings. I found that reference in Weber's book, too, and wonder if there is truth to it. But it looks like as with most things tube amp related, it depends what you mean by "better", and experimentation is your only real option mon frer.........

[Willabe]

I think the original question was, does a multi-tap secondary sound better using the highest impedance since it is using all the secondary windings. I found that reference in Weber's book,

Well, he does sell both OP tranys and speakers. So....


       Brad         

[HotBluePlates]

I personally think it's an over-extrapolation from a basic transformer-design issue.

Basic problem: it's easy to design a transformer with a 1:1 turns ratio that has excellent frequency response and low distortion; it's very hard to design a transformer with a very high turns ratio, because the parasitic elements (leakage inductance, leakage capacitance, etc) become big enough to have a major impact.

Tubes needs loads of at least several-hundred ohms to several-thousand ohms in their plate to efficiently transfer power. Our speakers range from a few-ohms to maybe a few-tens of ohms (Ampeg did use some 32 ohm speakers). That means a big turns ratio is needed.

The thought process is that the 16 ohm winding (most ohms) would have a lower impedance ratio to the primary (and so lower turns ratio) than the 4 ohm winding (least ohms). So the 16 ohm winding is better, right?

That's going a bit too far, in my opinion.

I think Marshall tended to use 16 ohm speakers/cabs for a different reason. In a combo, the length of wire to the speaker is a few inches. If you're making head/cabinet amps, use might have speaker cables that travel several feet to maybe 30ft or more (depending on stage setup). If the amp sees the total resistance of the speaker wire in series with the speaker resistance/impedance, then the longer cable becomes a bigger percentage of that total resistance. If you use a 4 ohm speaker load, the speaker cable (say 1 ohm total resistance) might become a significant portion of the total impedance, and waste output power; if you use a 16 ohm load, the same speaker cable (still 1 ohm) is insignificant.

I don't worry about which tap I use in a guitar amp, at least not for the turns-ratio/fidelity issue. It is what it is. I feel this tpoic was misapplying a bit of information, which then led to a silly conclusion, which was then presented as fact.

I'm grateful Gerald Weber wrote the books he did, because they were the first thing (only thing) I could get my hands on when I was trying to learn about tube amps (starting in the early-90's). But there is a lot that is presented as fact that is at best an incomplete picture, and also a healthy dose of self-serving advertising (he was building tweed copies at the time, so tweed amps/components were great and everything after garbage), which was also the case with Aspen Pittman's Tube Amp Books. I feel I've had to unlearn a lot of what I absirbs from those books.

[jojokeo]

I personally think it's an over-extrapolation from a basic transformer-design issue.

That's going a bit too far, in my opinion.

I don't worry about which tap I use in a guitar amp, at least not for the turns-ratio/fidelity issue. It is what it is. I feel this tpoic was misapplying a bit of information, which then led to a silly conclusion, which was then presented as fact.

+1
In my personal experiences I've used various output tubes & OTs and alternate btwn 4/8/16 taps depending on the output tube's Pri Z & speaker load. Many times the VERY slight difference that you may or may NOT hear can be so subtle or even not noticeable - that to worry about simply using one tap over another WITH the associated "matching" speaker Z is even less signifigant, IMHO.
Now some may argue that they can hear the difference btwn a House fly & a Fruit fly fart at 20 paces, even after playing for years in front of a Marshall stack or Fender Twin, but I beg to differ. In other words, whether using the 4r tap/4ohm speaker or 16r tap/16ohm speaker it is hardly worth thinking or worrying about.